Spraying devices of this type are to be found, for example, on what are referred to as field sprayers which are self-propelling or are conveyed behind towing vehicles and are used for applying crop protection agents. Field sprayers of this type conventionally have a foldable linkage, with working widths of up to 36 m being used. In the case of conventional field sprayers, a crop protection agent which is to be sprayed is mixed with water before the beginning of spraying, so that then a ready-mixed mixture of active compound and carrier liquid is present in a spray mixture tank. Conventional spraying devices of this type are problematic if the active compound concentration is to be changed during the spraying. Also if the crop protection agent to be sprayed is to be changed, the entire system has to be emptied and cleaned beforehand.